Production of wood pulp, etc.



Patented Feb. 2, 1932 UNITED STATES PATENT OFFICE H LINN BRADLEY, F MONTCLAIR, NEW JERSEY, AND EDWARD P. MCKEEI FE, OF PLATTS- 'BURG, NEW YORK, ASSIGNORS TO BRADLEY-MCKEEFE CORPORATION, 01' NEW YORK, I

N. Y., A. CORPORATION OF NEW YORK.

' PRODUCTION OF WOOD PULP, ETC.

No Drawing.

This invention relates totheproduction of wood pulp from wood and to the treatment of residual liquors from such operations and the production of cooking liquors for use in such operations, etc.

The. invention is applicable to a large variety of woods for the production of high grade chemical pulp therefrom for use in the manufacture of papers of various kinds and grades. The invention provides a regenerative process for utilizing the residual liquors for the production of further amounts of cooking liquor. The invention can be carried out in existing mill equipment, such as in the so-called sulphate pulp mills, but without the objectionable odors characteristic of such mills during operation. The invention makes possible the production of high grade pulps possessing good strength and felting properties and with high yields of pulp from various woods, ineluding woods not commonly considered available for the manufacture of high grade chemical pulp.

This application is a continuation in part of our prior applications Serial No. 434,720 filed January 3, 1921, Serial No. 456,187, filed March 28, 1921, Serial No. 481,146, filed June 28, 1921, Serial No. 534,768, filed-February/7, 1922. Serial No. 686.137, filed J anuary 14, 1924, Serial No. 704,176, filed April 4,. 1924, Serial No. 711,857, filed May 8, 1924, and SerialNo. 713,257, filed May 14, 1924.

According to the present invention, the cooking liquor contains caustic soda, sodium sulfite, and sodium sulfid, v. and'the amounts used are such that high grade chemical pulp is produced from the woods treated.

Our investigations indicate that when sodium hydroxide, sodium sulfite andsodium sulfid are utilized together in the cooking liquor the sodiumsulfite is less active than when it is used alone or with only small amounts of certain other ingredients; and that it is important for best results to have regulated amounts of the various chemicals present with reference to the wood treated. Our investigations indicate thatthe activity of sodium sulfite in the presence of sodium sulfid and caustic soda insubstantial amounts is only about one quarter theactivity of the sodium sulfid Application filed September 22, 1925. Serial No. 57,954.

and caustic soda, figured on an equivalent;- 'sodium content and we have developed the 3 following hypothetical reaction as possibly indicating the reaction of the sodium sulfite and sodium sulfid when so used 4Na SO 2N a. S 6H.Organic=' 6Na.Organic 3Na S O 3H O.

The residual liquors from the'process contain sodium thiosulfate or other sulfur containing compounds which readily set free sulphur when treated with acids, and the sulfate at the end of the reaction. While we do not desire to limit ourselves by any theoretical explanation of the reactions which take place, nevertheless the above hypothetical reaction seems not an improbable one in the process. i

In using the caustic soda, sodium sulfite and sodium sulfid in the cooking liquor, we have used an amount of sodium sulfite in which the sodium content was as much as or more than twice the sodium content of the sodium sulfid; while in other cases we have used cooking liquors in which the sodium present as sulfite was considerably less than the sodium content present as sulfid, e. g., as low as one-half the sodium content present as sulfid.

The sodium hydroxide used in the recess can be varied, but is in substantially a 1 cases leSs than suflicient to satisfactorily pulp the wood'if used by itself.

WehaXe found that if the sodium hydroxide, sodium sulfite and sodium sulfid are considered from the standpoint of their sodium content and this content expressed as sodium oxide, Na O, the total amount of sodium '02:- ide equivalent of the three ingredientsshould be such that that of the caustic soda and sodium sulfid, plus one quarter of the sodium oxide equivalent of the sulfite should be in excess of about 12.5%, by weight, ofthe bone dry weight of the wood treated, e. g., for pop lar wood, and in excess of about 15% based on the bone dry weight of the wood for spruce, pines, balsam, etc. Cottonwoodappears to require somewhat less than. poplar,

ut nearly all Woods require at least as much as poplar, while most of themrequire somewhat more. An excess of the chemicals can be used, particularly where a quicker cook is desired, and with resinous woods or Woods requiring an increased amount of the chemicals. The sodium oxide equivalents figured as aboveindicated '(i. e., the equivalent so dium oxide content of the sodium hydroxide and sodium sulfid plus one-fourth the sodium oxide equivalent of the sodium sulfite) and amounting to 16.5% or more, is sufficient to readily pulp most woods. The amount may be increased e. g. up to 25% or so.

In preparing the cooking liquor we consider that the caustic soda, as above indicated, is all active and in most cases we consider the sodium sulfid as all active, i. e. as entirely available for thechemical reaction of the process, especially when the sodium oxide content of the sodium sulfite present is at least equal to the sodium oxide equivalent of the sodium sulfid present. In calculating the activity of the sodium. sulfite, we consider about one-fourth of the sodium oxide content to be active or available in the reaction with the wood substance, so that we take as the total activity one-fourth of the sodium oxide content of the sulfite together with the sodium oxide content of the caustic soda and the sodium oxide equivalent of the sodium sulfid. As an exam le, for 100 parts of poplar Wood by weight (bone-dry basis), and using 12.31 parts of sodium hydroxide, 4 parts of sodium sulfid and 13 parts of sodium sulfite, the activity computed as above is equal to about 14.31% sodium oxide. From this example it is seen that allowance is made. for all of the sodium oxide content of the caustic soda and for all of the sodium oxide equivalent of the sodium sulfid and for approximately onefourth of the sodium oxide content of the sodium sulfite.

When the sodium oxide content of the sodium sulfite is somewhat more than twice the sodium oxide equivalent of the sodium sulfid, the excess sodium sulfite does not appear tobe active to any appreciable extent,

and allowance is made for only about one quarter of its sodium oxide content, so that this amount of sodium sulfite is equivalent to about one half of the sodium sulfid present. The sodium sulfite is nevertheless important in the process, particularly where there is arelatively high content of sodium sulfid. When sodium thiosulfate is permitted to react with wood it tends to give off elementary sulfur or to form dark colored compounds aeea voe unless there is :present sufficient sodium sulfite or other sulfur-dissolving compound capable of overcoming this objectionable tendency.

The cooking liquors containing substantial amounts of caustic soda, sodium sulfite and sodium sulfid may advantageously be prepared from the residual liquors of the process, e. g., by concentrating the residual liquors and subjecting them to a calcining or smelting operation with the production of a product from which sodium carbonate and sodium sulfid, with or without sodium sulfite, etc. may be dissolved. The solutioncontaining sodium carbonate, and sodium sulfid is advantageously treated with calcium hydroxide or lime and calcium sulfite in admixture with each other and with the amount and proportion of each so chosen as to yield a cooking liquor which will contain the desired amount of caustic soda, sodium sulfite and sodium sulfid. Where the recovered sodium compounds contain a preponderating amount of sodium carbonate and a considerably lesser amount of sodium sulfid, it is easy to prepare such a cooking liquor and to regulate the proportions of the ingredients. By treating part of the solution of the recovered sodium compounds with sulfur dioxide, some of the carbonate may be directly converted into sulfite, and some of the sulfid may be converted into thiosulfate, although by carrying out the sulfiting operating upon the hot liquor the formation of thiosulfate can be minimized. The content of sodium sulfid can to a certain extent be regulated and increased where desired by the addition of sodium sulfate or bisulfate to the residual liquor before thesmelting operation. Elementary sulfur may also be dissolved in the causticized solution, or it may be added to the hot solution of sodium carbonate and sodium sulfid before the causticizing and sulfiting treatment; or sulfur may be caused to react with calcium hydroxideand the re sulting product utilized for the causticizing treatment. Sodium sulfite'can be produced directly from sodium carbonate and sulfur dioxide and added to the cooking liquor. Where sulfur is aded to a caustic soda solution it is desirable in some cases to add it to caustic soda which does not contain sodium sulfite and to add the resulting solution to the sodium sulfite containing liquor so as to reduce the tendency of sodium sulfite to react with sulfur to form thiosulfate. Sodium thiosulfate may, however, be present in the cooking liquor, particularly where the amount of sodium sulfite is sufiicipntly high. ,1 The invention will be further J illustrated out with various woods, both deciduous and coniferous, and with cooking liquors of varying composition and activity, but all containing caustic soda, sodium sulfite and soby the following specific examples, carried dium sulfid in substantialamounts. These cooking liquors have been used in cooking the woods indicated, using a suflicient amount of liquor to submerge the chips and carrying out the cooking operations at a temperature corresponding to a saturated steampressure of 110 to 120 pounds gauge. The period of heating to bring the charge-up to pressure was about two hours and the cook was continued for about three and one-half to five and one-half hours, or until the cooking operation had been completed andthe fibres become readily separable.

The cooking liquors are given in the following examples in tabulated form, showing the actual parts by weight of caustic soda, sodium sulfid and sodium sulfite used, together with the parts by weight of wood (figured on bone-dry basis) and the particular Wood or mixture of Woods treated. At the top of each series of three examples the activity of the cooking liquor is indicated in percentage of sodium oxide and sodium sulfid equivalent based on the bone dry weight of the wood. The sodium oxide and sodium sulfid equivalents are calculated as hereinbefore described. That is, in calculating the sodium oxide equivalent, the sodium oxide content of the caustic soda is taken, together with the sodium oxide equivalent of the sodium 'sulfid,and one quarter of the sodium oxide content of the sodium sulfite. The sodium sulfid equivalent corresponds molecularly to the sodium oxide equivalent. These equivalents are used as a convenient means of expressing the activity of the cooking liquor with reference to the bone dry weight of the wood.

Computed activity Naz0012. 72 NazOel4. N820015. 3 Na2S 16. NazS 17. (l Nag-$019. 2

Ex. 1 Ex. 4 Ex. 7 NaOH 4. 313 4. 750 5. 003 N823 8. 429 9. 264 9. 756 NazSOa 6. 797 7. 483 7. 889 B. D. wood 85.0 poplar 85.5 poplar 82.5 poplar Ex. 2 Ex. Ex. 8 NaOH 4. 014 4. 416 4. 646 NazS 7. 814 8. 593 9. 055 NagSOz 12. 634 '13. 880 14. 614 B. D. wood 85.0 poplar 85.5 poplar 82. 5 poplar Ex. 3 Ex. 6 x. 9 NaOH 3. 508 3; 853 4. 060 NazS 6. 847 7. 519 7. 921 NagSOg 22. 115 24. 319 25. 589 B. D. wood 85.0 poplar 85.5 poplar 82.5 poplar NflaOOlQ. 1 Naz0$l2.7 Nflz0$14 0 N 813024. NazSe Na1So17 6 Ex. 10 Ex. 13 Ex. 16 NaOH 6. 785 6. 278 7. 057 N815 13. 232 6. 107 6. 865 NazSO; 10. 666 4. 939 5. 541 B. D. wood 89. 5 pine 81 2 poplar 83. 0 poplar and birch x. 11 Ex. 14 Ex. 17 NaOH 6. 302 5. 915 6. 655 NmS 12. 278 5. 777 6. 494 NaaSOi 19. 842 9. 326 10. 494 B. D. wood 89. 5 pine 81. 2 poplar 83. 0 poplar and birch Ex. 12 Ex. Ex. 18 NaOH 4. 994 5. 993 Nags 10. 741 4. 867 5. 846 NazSOz 34. 717 15. 714 18. 874 B. D. wood 89. 5 pine 76. 0 poplar 83. 0 poplar and birch Naz0 15 3 NazOelil. 1 NazOclQ. 1 Nazsow 2 NaS 24 NazSc x. 19 Ex. 22 Ex. 25 NaOH 8. 12 10. 144 10. 144 NazS 7. 914 9. 858 9. 856 NazSOa 6. 384 7. 978 7. 989 GB. D. wood 87. 5 poplar 87. 5 poplar 87. 5 spruce Computed activity-Continued Ex. 20 Ex. 23 Ex. 26 NaOH 7. 653 9. 573 9. 573. N azS 7. 459 9. 334 9. 339 NazSOs 12.062 15.083 15.078 B. D. wood 87. 5 poplar 87. 5 poplar 87.5 spruce Ex. 21 Ex. 24 Ex. 27 NaOH 6. 901 7. 485 8. 613 NazS 6. 714 7. 307 8. 399 NazSO; 21. 719 23. 587 27. 146 B. D. wood 87.5 poplar 76. 0 poplar 87. 5 spruce N810-C=12. 9 NazO$1-l. 0 NazO 15. 3 N 13.15016. 18 NazS017. 6 Na So19.2 1 Ex. 28 Ex. 31 Ex. 84 NaOH 8. 03 9. 143 9. 982 NazS 4. 701 5. 356 5. 848 Nags 0a 3. 803 4. 327 4. 733 B. D. wood 81 2 poplar 85 0 poplar 85. O poplar and birch X. 29 Ex. 32 EX. 35 NaOH 7. 705 8. 775 9. 568 N azS 4. 508 5. 132 5. 609 N82SO3 7. 275 8. 308 9.042 B. D. Wood 81. 2 poplar 85.0 poplar 85.0 poplar and birch Ex. 30 EX. 33 Ex. 36 NaOH 7.096 8. 073 8. 809 N825 4. 150 4. 729 5. 147' NazSOs 13. 309 15. 263 16. 652 B. D. wood 81. 2 poplar 85.0 poplar 85.0 poplar and birch Cooking liquor No. 1 contains about the minimum activity, computed as hereinbefore described. That is, all of the N a O of the NaOH and the N a S (on a Na O equivalent basis) and one fourth of the Na O content of the Na SO when added together equal about 16% Na s equivalent, or about 12.72% Na O, based on the bone dry weight of the wood treated. When the amount of Na s is so high and the NaOH and the Na SO are in the proportion given in this example, this wood isfairly well cooked. This same liquor upon cottonwood operates a little better than it does on poplar. There is not quite enough NagsOg to yield a light colored pulp. For cookingv resinous woods, the chemicals may be used in the same ratio but are advantageously increased in amount so that the activity as computed above is at least 19.2% N328 equivalent, or 15.26% Na O, on the B. D. wood weight.

Cooking liquor No. 2 contains NaOH and Na s in the same ratio as No. 1, but differs therefrom inhaving an equal amount of Na O equivalent in the sulfite as there is in the sulfid instead of one-half as much as shown in Example No. 1, and the amount of NaOH and of N5 8 has been slightly reduced so that the activity as computed herein remains substantially the same as in No. 1. This cooking liquor works somewhat better than the cooking liquor No. 1. For coniferous woods it is advantageous to increase the amount of chemicals so. that the activity is at least equal to 19.2% Na S equivalent, or. 15.26% Na O, on the B. D. weight of the Wood (calculated as above). I

Cooking liquor No. 3 has the same NaOH Na s ratios as No. 1 and No. 2 and the amount of chemicals is such that the computed activity is about the same, while the Na SO content is so increased that it contains twice as much Na O equivalent as the Na S. This cooking liquor works better than No. 1 and fil No. 2. (Where the Na s contentis relatively high incomparison with the NaQH,it is desirable to have a relatively high'content of Na SO so as to lessen the odors developed during cooking, to obtain lighter colored pulp and to furnish a higher content of Na s in the recovered soda than would be obtained if the Na SO content were kept low.

in cooking liquors like No. 3. Cooking liquor having such ratios as in Example No. 3 are very suitable for producing high quality stock provided the activity as computed is kept sufiiciently high. By keeping the ratio of NaOH-Nafi Na SO about constant, but increasing the amounts of each in proportion so that the computed activity is at least 18% Na s equivalent, or 14.31% Na O, for deciduous woods, and at least equal to 19.2% Na s equivalent, or 15.26% Na O for coniferous woods, excellent pulps, possessing splendid strength and of good color may be readily obtained.

It will be noted that in the cookin liquors of Examples No. 1, No. 2 and No. 3; t eNa O content of the NaOH is substantially one half the Na O content (equivalent) of the Na S,

and that the amount of Na SO compared with the Na S is chan ed so that it varies from one half as much Na content up to twice as much Na O content. It may also be pointed .outthat with such high Na s content it is advanta cons to use a relatively high content of Na s and, in fact, even an excess over the equation referred to previously; and that an activity of at least 18% Na s equivalent for deciduous woods is desirable in 'most instances, and an activity of at least 19.2% Na S equivalent is desirable for coniferous woods.

Tn cooking li uors No. 4, No. 5, and No. 6, the ratio of Na H to Na S is the same as in those numbered 1, 2 and 3, and the Na SO varies in amount, e. g. in N o. 4 having one half as much Na O as thereis in the Na S, in No. 5 having anequal'amount and No. 6 having twice as much Na O as the Na s. These three cooking liquors differ from the first three in having a higher computed activity, this being equvalent to about 17.6% Na S, or 14.00% Na O. That of No. 4 has less total sodium than either No. 5 or No. 6, for the same computed activity. No. 6 has a higher content of Na SO and has been found to yield pulps of somewhat lighter color than No. 4 and even than No. 5.v

Cooking liquors Nos. 7, 8 and 9 have the same ratio of NaO-H to Na S as in cooking liquors Nos. 1 to 6, i. e. one half as much Na U in the form of NaOH as there is in the form' of Na S, withthe Na O in the Na SO ranging from one half the Na o of the Na S, through an equal amount up to twice as much Na O in the Na SO as there is in the Na s. The computed activity in 7, 8 and 9 is sub- An even greater amount of Na SO can be used than erated cooking liquor. This feature is of particular importance where the soda losses are rather high and either Na SO or'NaOI-I or both are used for making up the losses of soda instead of sodium sulfate or nitre cake additions to the cycle.

In cooking liquors Nos. 10, 11 and 12 the ratios of NaOH to Na s and to Na SO are seen to be similar to those in 1, 2, 3, in 4, 5, 6, and in 7, 8 and 9, respectively, but the amounts of each reagent have been increased so that the computed activity is up to an equivalent of 25% Na s, or 19.08% Na O, calculated as above. This strength of cooking liquor, i. e. an equivalent of 24% Na S or 19.08% Na t) on the weight of the bone dry wood makes a is substantially equivalent to the Na S, while the activity in the first three, calculated as above, is equivalent to about 16% Na s, the activity in the second three, (16, 17 and 18) is equivalent to about 17.6% Na S, in the third group (19, 20 and 21) the activity is equivalent to about 19.2% Na s, and in the two latter groups (22 to 27) the activity, as computed herein, is equivalent to about 24% Na s on the bone dry weight of the wood. The amount of Na O in the Na SO in each group of three cooking liquors ranges from one half as much Na- O as is in the Na s, through an equal amount up to twice as much Na O in the Na S0 as there is in the Na s. Andeven greater amount of Na SO may be use These activities, expressed as above, range from about the lowest point which will satisfactorily cook wood in a single stage operation up to and including sufficient activity for cooking practically all woods which will be usedi in chemical pulp mills. The NaOH content of the liquor is equivalent to the Na S content in each example, while the Na SO is varied in proportion. The higher 3d, 35 and 36 are liquors in which the amount of Na O present as NaOH is materially greater'than the Na O equivalent of the.

Na S, and the activity as computed herein 5 ranges from 16.18% Na s equivalent through 17.6% Na S equivalent and includes three examples in which the activity is 19.2% 'Na S equivalent. The Na S ranges from an Na O content of one half that of the Na S through an equal amount up to and including an amount which is twice the Na content of the Na s. An even greater amount of Na SO may he used and this in advantageous especially when the lower activities are 5 employed and it is desired to obtain pulp of lighter color. I

In the last nine examples it'will be noted that less Na S is used and also less Na SO than the previous examplessince more cooking is due to the NaOH content. In cases Where the NaOH predominates over both the Na s and Na SO the amount of chemicals in the digester charge is generally less than is charged when a lower percentage of NaOH is used. Care should be taken, however, to keep the actual NaOH down below the point where the fibres are readily destroyed or objectionably injured.

The process of the present invention is advantageously carried out as a regenerative process by treating the residual liquors of the process for ,the production of "further amounts of cooking liquor therefrom. The residual liquors can be tre ated according to methods described in our prior a plications hereinbefore referred to, e. g. 'y concentrating the residual liquor, subjecting it to a calcining or smelting operation with resulting production of a product containing sodium sulfid and sodium carbonate, either with or without sodium sulfite etc., and this product can be dissolved or extracted to form a solution which can be treated to produce the cooking liquor. The solution can be treated, e. g., with calcium sulfite, to convert sodium carbonate into sodium sulfite, or with a mixture of calcium sulfite and calcium hydroxide to produce both sodium sulfite and caustic soda in regulated amounts. The solution can also be treated by various other procedures described in our said prior applications for the production of cooking liquors containing sodium sulfide, sodium sulfite, and caustic soda, in regulated amounts, either -'Na O, but less than 15.26%

with or without the production of sodium thiosulfate, etc.

Weclaim': f

1. The method of producing wood pulp from wood which comprises cooking the wood in. a cooking liquor comprising substantial amounts of sodium hydroxide, sodium sulfid and sodium sulfite, the sodium oxide'content of the sulfite being greater in amount than the sodium oxide equivalent of the hydroxide.

2. The method of producin wood pulp from'wood which comprises coo ing wood in a" cooking liquor comprising substantial .amounts of sodium hydroxide sodium sulfid and sodium sulfite, the sodium oxide content of the sulfitebeing greater than the sodium oxide equivalent of both the sulfid and the hydroxide. I

3. The method of producing wood pulp from wood which comprises cooking the wood in a cooking liquor comprising sodium hydroxide, sodium sulfid and sodium sulfite each of which constitutes a principal di esting rea cut, the sodium oxide content 0 the sulfite eing more than one-half and less than twice that of the sulfide, the activity, calculated as herein described, being at least 12.5% Na O, but less than 14% Na O, substantially as described.

.4. The method of producingwood pulp from wood which comprises cooking the wood in a cooking liquor comprising sodium hydroxide, sodium sulfid and sodium sulfite each of which constitutes a principal di esting reagent, the sodium oxide content 0 the sulfite being more than one-half and less than twice that of the sulfide, the activity, calculated as herein described, bein at least 12.5%

la o, substantially as described.

5. The method of producing wood pulp from wood which comprises cooking the wood in a cooking liquor comprising sodium hydroxide, sodium sulfid and sodium sulfite each of which constitutes a principal di esting reagent, the sodium oxide content 0 the sulfite being more than one-half and less than twice that of the sulfide, the activity, calcu-' lated as herein described, bein at least 12.5% Na O, but less than 16.53% lla O, substantially as described.

6. The method of producin wood pulp from wood which comprises coo ing the wood in a cooking liquor comprising sodium hydroxide, sodium sulfid and sodium sulfite each of which constitutes a rincipal di esting reagent, the sodium oxi e content 0% the sulfite being more than one-half and less than twice that of the-sulfide, the activity, calculated as herein described, being at least 12.5% Na' O, but less than 25% Na O, substantially as described. 1 n

7. The method of producing pulp from wood which comprises digesting wood by weaves means of a liquor containing substantial amounts of caustic soda, sodium sulfite and sodium sulfid, the activity of which shall be not less than l2 as defined above, and said liquor shall include not less than two molecules of sodium sulfite (Na SO for each molecule of sodium hydroxide (NaOl-l) 8. Method of producing wood pulp from wood, which comprises cooking the wood in my a cooking liquor comprising substantial amounts of sodium hydroxide, sodium sul fide and sodium sulfite, the sodium oxide content of the sulfite being greater in amount than the sodium oxideequivalent of either 5; the hydroxide or the sulfide and the sulfide being not less in amount than the hydroxide. th'llhe method of producing pulp from wood which comprises digesting wood by means of a liquor containing substantial amounts of sodium suliite, sodium sulfide, and sodium hydroxide, the sodium oxide equivalent of neither the sulfide nor the hydroxide being less than one-half nor more than equal to the sodium oxide equivalent as of the sulfite, and the activity calculated as herein described in excess of about l2,50%.

In testimony whereof we afix our signa-' tures,

LINN BRADLEY. an EDWARD MGKEEFE. 

